Not really no, You don't need to take the containers, just the contents, take it to somewhere hidden, keep the crew under guard, ferry off the food, or at least as much as you can, and then release the crew sans a load of cargo, if this was about the food itself, that is what the sensible course would be, because you don't want people finding out who you are, you are ashamed of being a thief, but it's a matter of survival.
This was a blatant announcement of 'We are thieves and we want money', I don't think any court in the world would buy 'hunger' as a defence.
That said, I'm not entirely sure that, as relief aid, this would be considered 'private property'.